The Yonaguni language (与那国物言/ドゥナンムヌイDunan Munui) is a Southern Ryukyuan language spoken by around 400 people on the island of Yonaguni, in the Ryukyu Islands, the westernmost of the chain lying just east of Taiwan.[3] It is most closely related to Yaeyama. Due to the Japanese policy on languages, the language is not recognized by the government, which instead calls it the Yonaguni dialect (与那国方言,Yonaguni hōgen). As classified by UNESCO, the Yonaguni language is the most endangered language in all of Japan.

^a [o] can also probably be recognized as an independent phoneme and not just as an allophone of /u/. However, its distribution is very limited. Excluding a few interjections, the only morpheme in which it appears is the sentence-final, exclamatory particle do.

The table below shows the consonants present in the Yonaguni language. Consonants which are only allophonic appear in parentheses. Plosive and affricate phonemes have three-way contrast between fortis, lenis, and voiced consonants.

As a Southern Ryukyuan language, Yonaguni, similar to Miyako and Yaeyama, has /b/ in place with Standard Japanese/w/, such as Yonaguni /bada/ ('stomach, belly'), cognate with Japanese /wata/ ('guts, bowels'). Yonaguni also has /d/ where Japanese and other Ryukyuan languages have /j/ (orthographically y). Thus, for example, Yonaguni /dama/ ('mountain') is cognate with Japanese and Yaeyama /jama/ ('id.'). Yonaguni /d/ is probably a recent development from an earlier */j/, however, judging from the fact that even the */j/ in loanwords of Sinitic origin is pronounced /d/ by speakers of the Yonaguni language.

The Yonaguni language exhibits intervocalic voicing of plosives, as do many Japonic languages. It also exhibits the tendency for /ɡ/, especially when intervocalic, to be pronounced as a velar nasal /ŋ/, as in Standard Japanese.

Yonaguni was once written with a unique writing system called Kaidā logograms. However, after conquest by the Ryukyu Kingdom and later annexation by the Empire of Japan, the logograms were replaced by Japanese kana and Chinese characters.